A board mountable differential signal transmission connector, in which contact sets (triplet) each constituted by a pair of differential signal transmission contacts and a single grounding contact in a triangular formation, with adjacent triplets being inverted with respect to each other, are provided in two rows of contacts in an engaging portion (PCT Japanese Publication No. 2004-534358). Twisted pair cables, in which positive signal lines and negative signal lines are twisted with each other, are utilized as cables to be connected to the differential signal transmission contacts, because these cables are suited for digital transmission. In an engaging portion of this differential signal transmission connector, the pair of differential signal transmission contacts of a first contact set that constitutes triplet, that is, signal contacts, is provided in a first row, and the grounding contact of the contact set is provided in a second row. Meanwhile, the grounding contact of a second contact set adjacent to the first contact set is provided in the same row as the pair of signal contacts of the first contact set, and the pair of signal contacts of the second contact set is provided in the same row as the grounding contact of the first contact set.
The arrangement of the signal contacts and grounding contacts in the two rows within the engaging portion are converted to a single row at a board connecting portion of the board mountable differential signal transmission connector. The contacts within the single row are connected to a circuit board by solder.
PCT Japanese Publication No. 2004-534358 is silent regarding a connector of a cable to be connected to the board mountable differential signal transmission connector. However, it is considered that the connector of the cable has a plurality of contact sets that form triplets that include differential signal transmission contacts and grounding contacts corresponding to those of the board mountable differential signal transmission connector.
Recently, digital signal transmission at speeds higher than those heretofore is in demand. For example, there is demand for digital signal transmission at speeds of 1 to 5 Gb/sec. Accompanying this demand, connectors which are capable of high speed digital signal transmission without generating skew (time differences in signal reception) and crosstalk, are also in demand. Generally, as the transmission frequency increases, current becomes concentrated toward the surfaces of core wires (conductors) of wires (surface effect). High speed digital signal transmission is transmission of high frequency signals. Accordingly, in cases that high speed digital signals are transmitted, the attenuation rate of signals becomes great, particularly when the lengths of cables become long. Therefore, large diameter signal cables having large core wire surface areas become necessary.
The concept of providing signal contacts and a grounding contact of a differential signal transmission connector to form a triangular shape is schematically illustrated in FIG. 10A. In FIG. 10A, small diameter wires d1 and d2, which are connected to signal contacts s1 and s2 in a first row, and a grounding wire dg, which is connected to a grounding contact G1, form a triangular shape. Wires of American Wire Gauge (AWG) #30 may be used as the wires d1, d2 and the grounding wire dg. Here, the pitch between the wires d1 and d2 is denoted as P. Meanwhile, it is not possible to connect large diameter signal wires D1 and D2 to the signal contacts s1 and s2 and to connect the grounding wire dg to the grounding contact G1, because the surfaces of the insulators of the wires D1 and D2 interfere with each other, as illustrated in FIG. 10B. The wires D1 and D2 may be AWG #24 wires. In FIG. 10B, the portions of the wires D1 and D2 that interfere with each other are illustrated by hatching. If the pitch P is increased, it will be possible to utilize the large diameter wires D1 and D2. However, this will cause a problem that the size of the connector in the direction that the signal contacts s1 and s2 are arranged will become larger. Generally, a predetermined number of wires must be provided within a limited space. Accordingly, it is not realistic to increase the pitch between the wires, which will result in the connector itself becoming larger. Additionally, as shown in FIG. 10B, single grounding contact is provided between the two closest contact sets, which are provided inverted from each other, in order to prevent crosstalk. However, there is a possibility that signal contacts of separate contact sets will become too close to each other, thereby generating crosstalk therebetween.